1. Field of the Disclosure
This disclosure relates generally to digital communication and, more particularly, to reduction of the peak-to-average power ratio of signals of a digital communication system.
2. Background of the Disclosure
Some types of signals for digital communication, for example, a multi-carrier signal, such as an orthogonal frequency division multiplexed (OFDM) signal or a discrete multi-tone (DMT) signal, by nature, has a large peak-to-average power ratio (PAPR) which can pose various problems such as reducing the efficiency of a high-power amplifier (HPA), increasing complexity of signal converters, and severely reducing the average signal power relative to constant envelope modulation techniques. The efficiency of the HPA can be reduced because, in order to avoid operating in the non-linear region of its voltage-current (V-I) characteristic, the HPA may operate with a large back-off from its peak power. The increased complexity of signal converters, such as analog-to-digital converters (ADCs) and digital-to-analog converters (DACs), results from the signal converters having large dynamic ranges that support a large PAPR. The severe reduction of the average signal power relative to constant envelope modulation techniques causes degraded performance and reduction in coverage range, as received signal strengths and signal-to-noise ratios (SNR) are lower.
Simplistic approaches to PAPR reduction that involve amplitude clipping suffer from the problem of peak re-growth. Multiple iterations can overcome this problem but at the expense of increased out-of-band radiation and significantly degraded bit error rate (BER). Besides, the out-of-band radiation cannot be closely controlled, which can cause interference and impair regulatory electromagnetic compliance (EMC).
Other techniques such as coding, tone reservation, tone injection, partial transmit sequences, selected mapping, interleaving, etc., may require modifications to a communication standard, thereby impairing their usefulness. Some of them also require the transmitter to send side information to the receiver, which may require modified receivers to receive and use the side information.
Another method, active constellation extension, does not require any standard modifications but has significantly increased complexity. Such increased complexity may require increased processing capabilities that increase cost.
The use of the same reference symbols in different drawings indicates similar or identical items.